David Wildstein, the former New Jersey official who oversaw the George Washington Bridge lane closings that caused traffic havoc for the city of Fort Lee, N.J. last September, said today that "evidence exists" that New Jersey Gov. Chris Christie knew about lanes closing as they were happening.

Christie has denied knowing that the lanes were being shut down and that he learned about the chaos "after it was over." The lane closures caused massive gridlock for several days in Fort Lee, N.J., and for New York City commuters.

In the letter, first reported by the New York Times and obtained by ABC News, Wildstein writes "evidence exists...tying Mr. Christie to having knowledge of the lane closures, during the period when the lanes were closed, contrary to what the Governor stated publicly in a two-hour press conference...Mr. Wildstein contests the accuracy of various statements that the Governor made about him and he can prove the inaccuracy of some."

Christie, a Republican, and some of his aides were accused of closing the bridge lanes to punish the Democratic mayor of Fort Lee who had declined to endorse him for reelection.

Wildstein, a former high school classmate of Christie, was a member of the Port Authority, an quasi-governmental agency that oversees New York-New Jersey infrastructure, including bridges and tunnels.

The letter does not specify the evidence, but it is the first sign that Christie, a potential 2016 Republican presidential candidate, may have been aware of the closings.

In a press conference earlier this month Christie said, "there's no way that anybody would think that I know about everything that's going on, not only in every agency of government at all times."

"So what I can tell you is if people find that hard to believe, I don't know what else to say except to tell them that I had no knowledge of this -- of the planning, the execution or anything about it -- and that I first found out about it after it was over," Christie said.

The governor's office issued a statement today saying that he had "absolutely no prior knowledge of the lane closures before they happened and whatever Mr. Wildstein's motivations were for closing them to begin with," and that he "denies Mr. Wildstein's lawyer's other assertions."

The statement in full reads: "Mr. Wildstein's lawyer confirms what the Governor has said all along - he had absolutely no prior knowledge of the lane closures before they happened and whatever Mr. Wildstein's motivations were for closing them to begin with. As the Governor said in a December 13th press conference, he only first learned lanes were closed when it was reported by the press and as he said in his January 9th press conference, had no indication that this was anything other than a traffic study until he read otherwise the morning of January 8th. The Governor denies Mr. Wildstein's lawyer's other assertions."

The Star-Ledger, New Jersey's largest newspaper, said Christie should resign if Wildstein's allegation proves to be true.

The lane closings have spawned several investigations. The state legislature is investigating and has sent subpoenas to Wildstein and 17 other people, as well as Christie's administration and his re-election campaign.

The U.S. Attorney's office has also announced its own review of the biggest scandal of Christie's administration.

Earlier this month, Hoboken, N.J., Mayor Dawn Zimmer alleged that Christie's Lt. Gov. Kim Guadagno threatened her by saying that she would withhold Sandy relief money to the city of Hoboken unless the mayor backed a development project favored by the governor. The Christie administration vigorously denied that claim, calling it libelous.